This invention relates to single channel communications systems, particularly radio communications systems. Reference is made to two additional copending application, Ser. Nos. 564,855 and 564,634, filed on the same date as the present application and which contain related subject matter.
Direct mobile-to-mobile radio communication is limited in range by low antenna heights and relatively low power transmitters. In order to overcome these limitations and cover larger geographical areas, the concept of a single channel "community repeater" has developed whereby a receiver is coupled to a higher power transmitter at a location of favorable radio propagation. Signals from a mobile radio transmitter are received by the community repeater receiver and routed to the community repeater transmitter for rebroadcast to receiving mobiles. Many diverse groups of mobile users in the same community can utilize the same "repeater" by transmitting and receiving on the appropriate frequencies. Generally, the type of communication on a community repeater is a "push-to-talk, release-to-listen" message transmission of short duration between one mobile user and a kindred group of at least one other mobile user.
Crowded conditions can develop on the single communications channel as many different groups consisting of many mobile users attempt to use the channel. Common courtesy is often abandoned as mobile users transmit simultaneously in an effort to capture the channel and communicate their message. Mobile users who listen for a message directed to them or their group are exposed a cacophony of messages which are not of interest and may obscure the desired message.
To improve this situation, a number of developments, which are now well known, have been made. Common communication groupings or "fleets" of mobiles are formalized with special coding schemes such as continuous subaudible signals or precursor signals which are transmitted by a mobile to activate otherwise muted receivers of other members of its fleet. Directed calls of this sort reduce annoyance to the mobile user, for he no longer has to listen to every message on the channel, but they add to his operating burden as he must monitor the channel before transmitting. Also, even with these developments, access to the channel remains uncontrolled and contentious.
Coordinated multichannel radio systems, also well known, have provided better control of communications by automatically trunking a large number of user groups on a plurality of communication channels. Users in these systems automatically request service from a controlling means and receive a channel assignment and permission to transmit from the controlling means before being allowed to transmit on one of the channels. Although these systems are effective in reducing contention, the multi-channel operation protocol used by these systems is simply unusable for a single communication channel.
In addition to radio systems, the expanding field of multi-terminal processing has also generated an extensive need for sharing a scarce resource, i.e. a computer need for sharing a scarce resource, i.e. a computer processor, among a large number of users. Time-sharing systems, which have been developed as a result of this need, typically place both request for service and message in a storage queue where they are subsequently analyzed by an allocation mechanism for eventual assignment to the computer processor. Unlike the present invention, which must coordinate the requesting process with real time message transmission on the single communications channel, the scarce computer processor resource is aloof from the requesting process and operates on the message in other than real time.
The present invention, for the first time, affords real time community repeater users and other users of a single channel relief from the aggravations of a crowded communications channel. Users' satisfaction improves once contention for this channel is handled automatically and once necessary user manipulations of the mechanics involved in obtaining service on the channel are reduced. In addition, channel efficiency is increased as more mobiles can be accommodated on the single communications channel due to the automated control exercised and the reduction of the need to repeat messages due to interference.